All atoms of the element potassium have 19 protons. One of the most stable types of potassium atoms has the mass number 39.

How many neutrons make up one of these potassium atoms?

20

Explanation:

number of protons + number of neutrons = mass of atom

19+n=39

n=39-19=20

number of neutrons=20

Number of neutrons in potassium atoms is 20.

Explanation:

Given that,

Number of protons in all atoms of Potassium, Z = 19

Mass number of potassium atom, A = 39

We need to find the number of neutrons make up one of these potassium atoms. We know that the mass of an atom is equal to the sum of number of protons and number of neutrons. So,

A = Z + N

N is number of neutrons

N = A - Z

N = 39 - 19

N = 20

So, there are 20 neutrons in potassium atom. Hence, this is the required solution.